1. Technical Field of the Invention
The present invention relates to substrate processing method and apparatus for cleaning substrates to be processed, for example, semiconductor wafers, LCD glass substrates, etc. by immersing the substrates in cleaning liquids, e.g. chemicals, rinsing liquids, etc. and subsequently drying the cleaned substrates.
2. Description of the Related Art
Generally, in the manufacturing process of semiconductor devices, there is a widely-adopted cleaning method by which the substrates to be processed, for example, the semiconductor wafers, the LCD glass substrates, etc. (called xe2x80x9cwafers etc.xe2x80x9d hereinafter) are successively immersed in a cleaning bath filled up with a processing liquid, for example, the chemical, the rinsing liquid, or the like.
Further, such a cleaning apparatus is equipped with a drying unit which exposes the surfaces of the cleaned wafers etc. to dry gas of volatile organic solvent, such as IPA (isopropyl alcohol). In this unit, the vapor of dry gas is condensed or absorbed on the waters"" surfaces so that the moisture can be removed from the wafers etc.
As the conventional cleaning and drying apparatus of this kind, there is a known cleaning/drying apparatus which includes a cleaning bath (cleaning chamber), a drying section and moving means, for example, a wafer boat. In this apparatus, the cleaning bath stores and accommodates the rinsing liquid (cleaning liquid), for example, the chemical of hydrofluoric acid, pure water, etc. in order to immerse the substrates, such as semiconductor wafers W, in the stored liquid. The drying section is positioned above the cleaning bath. The wafer boat carries the plural number (e.g. 50 pcs.) of wafers W to bring them to the interior of the cleaning bath and the drying section.
While, as the conventional drying method, there are known techniques disclosed in Japanese Unexamined Patent Publication (kokai) No. 2-291128 and Japanese Examined Patent Publication (kokoku) No. 6-103686.
In the publications, the drying technique disclosed in Japanese Unexamined Patent Publication (kokai) No. 2-291128 is embodied in a process flow shown in FIGS. 10A-10E. That is, wafers W are firstly dipped in a treatment bath 2 overflowing with cleaning liquid, for example, pure water. During the immersion, inert gas, such as N2 gas, is charged into a processing chamber 3 for atmospheric interchange (FIG. 10A).
Next, dry gas 4 of volatile solvent vapor, such as IPA (isopropyl alcohol), is charged into the processing chamber 3 to form an IPA membrane on the surface of pure water (FIG. 10B). Then, the wafers W are pulled up from the treatment bath 2 into the processing chamber 3 by wafer carrying means, for example, a wafer boat 5.
Consequently, the withdrawn wafers W are brought into contact with the IPA gas and therefore, owing to the Marangoni""s effect (difference in surface tension), the vapor of dry gas 4 is condensed or absorbed on the waters"" surfaces to remove moisture from the wafers W for dry (FIG. 10C). Thereafter, N2 gas is supplied into the processing chamber 3 for removal of IPA gas in the chamber 3 (FIG. 10D) and furthermore, the interior of the processing chamber 3 is depressurized to progress the evaporation of residual moisture and IPA adhering to respective grooves of the wafer boat 5, completing the drying process (FIG. 10E).
As mentioned above, according to the conventional drying method of this kind, the removal of moisture on wafers and sequential drying are completed by the following steps of: dipping the wafers in the pure water for cleaning; moving the wafers and the pure water relatively thereby to allow the IPA membrane on the pure water surface and dry gas (IPA gas) to contact with the wafers"" surfaces; and condensing or absorbing the vapor of dry gas.
In the above drying method using the vapor of volatile organic solvent, such as IPA (isopropyl alcohol), it is preferable in aspect of drying effectiveness. However, it is troublesome to discharge or drain the organic solvent while causing the undesirable situation against the environment. Additionally, in order to ensure the safety, it is necessary that the processing apparatus is equipped with a CO2 extinguisher or the like.
Further, in the moisture removing method utilizing the Marangoni""s effect (difference in surface tension), the drying efficiency is not satisfactory so much.
Accordingly, it is therefore an object of the present invention to provide a substrate processing method and a substrate processing apparatus, by which it is possible to remove the processing liquid from the substrate without using such an organic solvent, appropriately.
The first feature of the invention resides in a substrate processing method for processing a substrate, comprising the steps of: immersing the substrate in processing liquid; and exposing the substrate out of the processing liquid, while the processing liquid is subjected to both electric field and magnetic field in order to apply an electromagnetic force to the processing liquid; whereby the processing liquid is removed from the surface of the substrate.
That is, the present invention provides the substrate processing method utilizing the electromagnetic force (Lorentz""s force) brought by the formation of both magnetic field and flow of electric current in the vicinity of the water surface, the method being different from the conventional substrate processing method, for example, the conventional cleaning/drying method. With the adoption of the xe2x80x9csurface-dryxe2x80x9d system without using any organic solvent, the present invention has merits to facilitate the handling of the substrate processing apparatus employing the above system and reduce the number of particles sticking to the substrate.
The second feature of the invention resides in that the processing liquid is subjected to the electric field and the magnetic field so that the resultant electromagnetic force has a downward component.
It is supposed that, for example, if drawing up the semiconductor wafer W (as the substrate) from the cleaning chamber (as the processing chamber) to the drying chamber, then the cleaning liquid (as the processing liquid) adheres to the substrate""s (wafer W) surface up to its portion somewhat higher than the level of the cleaning liquid due to the inherent surface tension, as shown in FIG. 3. Therefore, when the downward electromagnetic force F is applied perpendicularly or obliquely to the surface of the cleaning liquid by the adoption of magnetic field B and current I of FIG. 3, it is possible to eliminate the cleaning liquid adhering to the surfaces of the substrate effectively.
The third feature of the invention resides in that the processing liquid is subjected to the electric field and the magnetic field so that the resultant electromagnetic force has a downward component and horizontal component which directs from a reverse face to a pattern face of the substrate.
Thus, it is possible to give the processing liquid adhering to the substrate""s pattern face a force in a direction to separate the liquid from the face thereby to perform the removal of the processing liquid effectively.
The fourth feature of the invention resides in that the processing liquid is subjected to the electric field and the magnetic field so that the direction of the resultant electromagnetic force is changed as the substrate moves in relative to the surface of the processing liquid.
Therefore, in spite of irregularities on the substrate""s surface, it is possible to vary an operative direction of the electromagnetic force in accordance with the profile of the substrate""s surface, accomplishing the removal of the processing liquid sufficiently.
The fifth feature of the invention is bringing gas which ionizes the processing liquid to facilitate the flowing of an electric current therein into contact with the processing liquid.
Thus, in spite of pure water as the processing liquid, it is possible to provide the pure water with fine conductivity, so that the electromagnetic force can be produced more effectively.
The sixth feature of the invention resides in that the above gas contains either CO2 gas or mixed gas of CO2 and N2.
The seventh feature of the invention resides in that at least one of magnitude of the electric field and magnitude of the magnetic field is changed so as to vary the resultant electromagnetic force.
According to the feature, the variation in magnitude of the downward electromagnetic force allows the processing liquid to be vibrated to eliminate the processing liquid effectively.
The eighth feature of the invention resides in that the electric filed and the magnetic field are synchronized so as to produce the electromagnetic force in a regular direction. This feature allows pulsating currents or alternating currents to be employed for respective sources for electrical field and magnetic field.
The ninth feature of the invention resides in that warm water is employed as the processing liquid.
The tenth feature of the invention resides in that the substrate is coated with an protective oxidation film in the immersing step. Thus, owing to the positive formation of protective oxidation film on the substrate before the drying process, it is possible to protect the substrate from the subsequent drying process etc.
The eleventh feature of the invention resides in that before forming the protective oxidation film on the substrate, the substrate is subjected to a chemical process using hydrofluoric acid to removing the natural oxidation film which should be removed.
It is noted that the surface of the wafer, of which natural oxidation film has been already eliminated, is so activated that a natural oxidation film is easy to be formed on the surface. Nevertheless, according to the eleventh feature, since the substrate is positively coated with a clean protective oxidation film after deleting the previous natural oxidation film, it is possible to restrict the formation of the natural oxidation film.
The 12th feature of the invention resides in the substrate processing apparatus for processing a substrate, comprising: a processing bath for storing a processing liquid in which the substrate is to be processed;
exposure means for exposing the substrate out of the processing liquid in the processing bath; electrodes arranged in the vicinity of a surface of the processing liquid stored in the processing bath for generating an electric current in the processing liquid in the processing bath; and magnetic poles arranged for generating a magnetic field in a direction different from the flowing direction of the electric current.
The 13th feature of the invention resides in that the magnetic poles each include a core and a magnetic coil wound about the core and also connected to an alternating current power source, while the electrodes are also connected to an alternating current power source.
With the above-mentioned constitution, when drawing up the substrate out of the processing chamber, there is produced a force between the surface of the substrate and processing liquid, which causes the processing liquid to adhere to the substrate due to the surface tension. This force is restricted by the downward electromagnetic force (i.e. Lorentz""s force) produced by the electrode plates and the electromagnetic coils. Thus, the above force is weakened in appearance to complete the appropriate removal and drying. Owing to the adoption of the xe2x80x9csurface-dryxe2x80x9d system without using any organic solvent, the present invention has merits to facilitate the handling of the apparatus and reduce the number of particles sticking to the substrate.
The 14th feature of the invention resides in that the exposure means includes a moving mechanism for moving the substrate from the processing bath upward while carrying the substrate. Additionally, the 15th feature of the invention resides in that the exposure means includes a drain port formed in the bottom of the processing bath, a drain pipe connected to the drain port and an opening-closing valve interposed in the drain pipe. Thus, any element would be applicable to the exposure means if only it can move the substrate in relation to the surface of the processing liquid.
The 16th feature of the invention resides in that the electrodes and the magnetic poles are arranged so that an electromagnetic force generated in the processing liquid by the electric current and the magnetic field possesses a downward component.
It is supposed that, for example, if drawing up the substrate from the cleaning chamber to the drying chamber, then the cleaning liquid adheres to the substrate""s surface up to its portion somewhat higher than the level of the cleaning liquid due to the inherent surface tension. Therefore, when the downward electromagnetic force is applied perpendicularly or obliquely to the surface of the cleaning liquid, it is possible to eliminate the cleaning liquid adhering to the surfaces of the substrate effectively.
The 17th feature of the invention resides in that the electrodes include a pair of electrode parts which are arranged in the processing bath so as to oppose each other in the vicinity of a surface of the processing liquid stored in the processing bath; the magnetic poles include a pair of magnetic pole parts which are arranged so as to oppose each other in the vicinity of a surface of the processing liquid stored in the processing bath; and the opposing direction of the electrode part s in pairs a nd the opposing direction of the magnetic pole parts in pairs intersect with each other.
Accordingly, it is possible to exert the downward electromagnetic f orce on the surface of the processing liquid, accomplishing the removal of the liquid from the surface effectively.
The 18th feature of the invention resides in that the electrodes include a pair of electrode parts which are arranged in the processing bath so as to oppose each other in the vicinity of a surface of the processing liquid stored in the processing bath; the magnetic poles include a pair of magnetic pole parts which are arranged so as to oppose each other and also arranged so that the opposing direction of the magnetic pole parts intersects with the opposing direction of the electrode parts; and the magnetic poles are arranged so that the magnetic polar parts can occupy an optional rotating position around the opposing direction of the electrode parts, as a rotational axis.
Therefore, it is possible to rotate the direction of the magnetic field around the opposing direction of the pair of electrodes, as the rotational axis.
The 19th feature of the invention resides in that the substrate processing apparatus of the above 12th feature further comprises a pipe for supplying the processing liquid into the processing bath and at least either one of ozone water generating means interposed in the pipe, for generating ozone water and water heating means interposed in the pipe, for heating water to be a warm water.
According to the constitution, it is possible to form a clean oxidation film on the substrate easily and positively before drawing up the substrate.
The 20th feature of the invention resides in that the substrate processing apparatus of the above 12th feature further comprises a cover which closely surrounds the upside of the processing bath thereby to define a drying chamber above the processing bath and that the drying chamber is provided, at an interior thereof, with a gas supply port which is connected to a gas supply source.
The above constitution allows either CO2 gas or the mixture of CO2 and N2 to be supplied to the processing liquid, so that it can be ionized to facilitate the formation of electric current or liquid flow.
The above and other features and advantages of this invention will become apparent, and the invention itself will best be understood, from a study of the following description and appended claims, with reference had to the attached drawings showing preferred embodiments of the invention.